Balanced Field Length
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Mad (Flt) Scientist
I agree, but one does not choose the V 1 so the ASD to meet the ASDA.
V1 is selected so ASD=TOD and that's what balanced take off is all about.
To state that balanced take means that ASDA=TODA is the same as to state that IF a takeoff is balanced then you are limited by the runway lenght and that's not true at all.
This is clearly indicated on any RTOW chart.
I agree, but one does not choose the V 1 so the ASD to meet the ASDA.
V1 is selected so ASD=TOD and that's what balanced take off is all about.
To state that balanced take means that ASDA=TODA is the same as to state that IF a takeoff is balanced then you are limited by the runway lenght and that's not true at all.
This is clearly indicated on any RTOW chart.
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... one does not choose the V1 so the ASD to meet the ASDA. V1 is selected so ASD=TOD and that's what balanced take off is all about.
To state that balanced take means that ASDA=TODA is the same as to state that IF a takeoff is balanced then you are limited by the runway lenght and that's not true at all.
This is clearly indicated on any RTOW chart.
To state that balanced take means that ASDA=TODA is the same as to state that IF a takeoff is balanced then you are limited by the runway lenght and that's not true at all.
This is clearly indicated on any RTOW chart.
In fact, a BFLR aircraft is more likely to be restricted by the runway than a non BFLR aircraft unless the field itself is balanced i.e. BFLA. So the two concepts do have a linkage.
BFL(R) is a simplification for ease of use, just as much as BFL(A) is. In both cases you are giving up some flexibility in scheduling speeds (and hence losing efficiency of operations) in order to obtain simplification.
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Balanced take off has nothing to do with characteristics of an airfield but everything with the actual performance of the aircraft in terms of a chosen V1.
Once these data are set they are compared to the TODA and ASDA to make the take off legal but these are two different issues.
The calculation of V1 so TOD=ASD is the only process that balances the take off, verifying that the TOD and ASD are lower than TODA and ASDA in not a performance calculation at all, as such there is only one correct definition and it's important that this is clearly understood.
Once these data are set they are compared to the TODA and ASDA to make the take off legal but these are two different issues.
The calculation of V1 so TOD=ASD is the only process that balances the take off, verifying that the TOD and ASD are lower than TODA and ASDA in not a performance calculation at all, as such there is only one correct definition and it's important that this is clearly understood.
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If you take a B 737 at 50 ton its impossible to choose a V1 that would make the balanced TOD equal to a TODA in case of a 4000 m runway.
The error in your reasoning is that you mix the actual performance calculation with the runway characteristics.
Calculations are done for each temperature at max available thrust for the prevailing conditions until the highest weight is found with an associated V1 that balances the associated TOD and ASD.
After this calculation is finished it is compared to the TODA and ASDA, these distances may very well be much greater than the calculated TOD and ASD for the limiting temp and thrust. As a consequence you have a balanced take off were TOD < TODA and ASD < ASDA
Ref: Dr Prof JJ Ruijrok Delft University Section Design and Flight Mechanics research in Aircraft Performance, Propulsion and Noise.
The error in your reasoning is that you mix the actual performance calculation with the runway characteristics.
Calculations are done for each temperature at max available thrust for the prevailing conditions until the highest weight is found with an associated V1 that balances the associated TOD and ASD.
After this calculation is finished it is compared to the TODA and ASDA, these distances may very well be much greater than the calculated TOD and ASD for the limiting temp and thrust. As a consequence you have a balanced take off were TOD < TODA and ASD < ASDA
Ref: Dr Prof JJ Ruijrok Delft University Section Design and Flight Mechanics research in Aircraft Performance, Propulsion and Noise.
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Look, I'm not saying your definition is wrong and I do understand how it works, thank you. All I'm asking you to accept is that a second definition exists. I can show it to you in regulatory documents if that would help.
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Just by stating and repeating that there are WMD in I*** does not mean that you will find them;
British nonsense, same with your statement about ASDA and balanced take off.
And it is not my definition, it\'s the way things are done. BASTA.
British nonsense, same with your statement about ASDA and balanced take off.
And it is not my definition, it\'s the way things are done. BASTA.
Moderator
.. I'm not too fussed about who wins an argument when the argument relates to semantics.
However, if the tone deteriorates any further, either the relevant poster(s) will be constrained or the thread will be locked.
Please keep in mind that we play the ball here .. not the player.
However, if the tone deteriorates any further, either the relevant poster(s) will be constrained or the thread will be locked.
Please keep in mind that we play the ball here .. not the player.
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Girls, girls, girls,
Alex and CAP56, you are both right. You will see from my previous post that I tried to explain BFL in terms of selecting V1 to balance the ASDR & AGDR........this is the American way of doing things.
I had to refer back to my books(The Aircraft Performance Requirements Manual by RV Davies). According to this book the Brits do say that a Balanced Field exists when ASDA = AGDA.
This was was a revelation to me! I have to now sit down and rethink a subject I thought I understood. I am not sure why they did it this way, but I am sure we can get to the bottom of it.
KTK
Alex and CAP56, you are both right. You will see from my previous post that I tried to explain BFL in terms of selecting V1 to balance the ASDR & AGDR........this is the American way of doing things.
I had to refer back to my books(The Aircraft Performance Requirements Manual by RV Davies). According to this book the Brits do say that a Balanced Field exists when ASDA = AGDA.
This was was a revelation to me! I have to now sit down and rethink a subject I thought I understood. I am not sure why they did it this way, but I am sure we can get to the bottom of it.
KTK
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I think the concepts are the same. As the Mad (Flt) Scientist neatly summarised above the difference only lies in the definitions.
The B737 charts I have to hand input 'Field Length Available' (I'm assuming this is TORA=TODA=ASDA) to output FLL TOM. A second set of tables take density altitude and TOM to derive a V1. The whole arrangement seems designed for simplicity at the possible expense of accuracy. The British balanced field charts of the '50s and '60s, not just the V bombers - I used them only as an example, are identical in concept. The only issue is the definition, the Americans refer to a balanced field as occurring when TODR=ASDR, the Brits when TODA=ASDA.
The B737 charts I have to hand input 'Field Length Available' (I'm assuming this is TORA=TODA=ASDA) to output FLL TOM. A second set of tables take density altitude and TOM to derive a V1. The whole arrangement seems designed for simplicity at the possible expense of accuracy. The British balanced field charts of the '50s and '60s, not just the V bombers - I used them only as an example, are identical in concept. The only issue is the definition, the Americans refer to a balanced field as occurring when TODR=ASDR, the Brits when TODA=ASDA.
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john_tullamarine
It is not about semantics at all.
If you do not see that, you have not understood anything and I am not surprised.
Boeing publishes simplified tables, the real calculations are done by computer and if you know how the software is programmed it becomes all very clear.
Any performance engineer who would give Alex Whittingham's definition would fail his exam.
Alex Whittingham
By using the charts, the way you describe; you only calculate the balanced MTOW and associated V1for a particular runway under certain prevailing conditions and that was not what the original question referred too.
As such you do not answer the question hence you fail the question on the exam.
If the question would have been “calculate the max TOW for a particular runway” the Alex argument is correct. However balanced take off does NOT mean that at all times you are limited by the ASDA and the Brits are wrong if they claim this to be the case.
REf: Pierre Volosin, Boeing Performance engineer.
So finally there seems to be a British definition that is NOT accepted on the continent as is the case with many other issues that are not accepted on the continent.
I have had to deal with this attitude before and sometimes there is simply no way you can get trough their thick scull until an incident happens and all the **** comes to the surface.
I am sorry I have to put it like this but that’s the way it is.
(word deleted - site policy)
It is not about semantics at all.
If you do not see that, you have not understood anything and I am not surprised.
Boeing publishes simplified tables, the real calculations are done by computer and if you know how the software is programmed it becomes all very clear.
Any performance engineer who would give Alex Whittingham's definition would fail his exam.
Alex Whittingham
By using the charts, the way you describe; you only calculate the balanced MTOW and associated V1for a particular runway under certain prevailing conditions and that was not what the original question referred too.
As such you do not answer the question hence you fail the question on the exam.
If the question would have been “calculate the max TOW for a particular runway” the Alex argument is correct. However balanced take off does NOT mean that at all times you are limited by the ASDA and the Brits are wrong if they claim this to be the case.
REf: Pierre Volosin, Boeing Performance engineer.
So finally there seems to be a British definition that is NOT accepted on the continent as is the case with many other issues that are not accepted on the continent.
I have had to deal with this attitude before and sometimes there is simply no way you can get trough their thick scull until an incident happens and all the **** comes to the surface.
I am sorry I have to put it like this but that’s the way it is.
(word deleted - site policy)
Last edited by john_tullamarine; 2nd Sep 2004 at 22:50.
However balanced take off does NOT mean that at all times you are limited by the ASDA and the Brits are wrong if they claim this to be the case.
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The difference is that you can balance a take-off but you can not balance a field length.
That is, you can not balance a ASDA nor TODA it\'s just a distance.
To balance the take off means to take the action or imply the condition in choosing a V 1 so TOD=ASD thats all.
That is, you can not balance a ASDA nor TODA it\'s just a distance.
To balance the take off means to take the action or imply the condition in choosing a V 1 so TOD=ASD thats all.
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Sorry, cap_56, but you can balance a field.
Either you do it in actuality, by means of construction of the airfield such that ASDA and TODA are, in fact, equal - which obviously you CANNOT do on a day-by-day basis - or you can assume the field to be balanced, by assuming that BFLA=min(ASDA,TODA), which, taken in conjunction with data relating field performance to (balanced) filed length requirements - the BFL you are using - enables a simplified assessment of the takeoff conditions to be undertaken.
In fact, if all that is available for take off performance data are BFL (required) then you have to assume a balanced field available because you have no way to take credit for the excess ASDA or TODA, as you have no ASDR or TODR data.
Either you do it in actuality, by means of construction of the airfield such that ASDA and TODA are, in fact, equal - which obviously you CANNOT do on a day-by-day basis - or you can assume the field to be balanced, by assuming that BFLA=min(ASDA,TODA), which, taken in conjunction with data relating field performance to (balanced) filed length requirements - the BFL you are using - enables a simplified assessment of the takeoff conditions to be undertaken.
In fact, if all that is available for take off performance data are BFL (required) then you have to assume a balanced field available because you have no way to take credit for the excess ASDA or TODA, as you have no ASDR or TODR data.
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or you can assume the field to be balanced, by assuming that BFLA=min(ASDA,TODA), which, taken in conjunction with data relating field performance to (balanced) filed length requirements - the BFL you are using - enables a simplified assessment of the takeoff conditions to be undertaken.
Twisted reasoning to prove a point that has no relevance.
I realise I am involved with some Brits that can not accept a simple truth.
I just hope that the chap that raised the question does not get completely confused by your assumptions.
Cheers and good luck with your B-Levels
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Flying clog
In the land of the JAA...
And to answer the question at interview I would suggest the following:
"Both the TODR and the ASDR increase with increasing mass. The MTM at a given runway is obviously achieved by selecting the V1 value so that the TODA and the ASDA are of equal length."
"When both the required distances are of equal length the take off is said to be a balanced field length take-off. The balanced field length take off method is normally used because it gives the highest allowable take-off mass for the available runway."
I am quoting from the BAE notes (thanks to Graham Morris who is in the UAE somewhere I think and flew V bombers)
In the land of the JAA...
And to answer the question at interview I would suggest the following:
"Both the TODR and the ASDR increase with increasing mass. The MTM at a given runway is obviously achieved by selecting the V1 value so that the TODA and the ASDA are of equal length."
"When both the required distances are of equal length the take off is said to be a balanced field length take-off. The balanced field length take off method is normally used because it gives the highest allowable take-off mass for the available runway."
I am quoting from the BAE notes (thanks to Graham Morris who is in the UAE somewhere I think and flew V bombers)
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Theoretical world meets the real world. Alex your answer is correct as per the requirements of the written exams, however as soon as someone sits in a FMS equipped aircraft or uses QRH V-speed values, CAP56 is correct.
Now aren’t we all glad that Flying Clog asked for the simple explanation
Benhurr, I most certainly wouldn’t give that answer for an interview!
Mutt.
Now aren’t we all glad that Flying Clog asked for the simple explanation
Benhurr, I most certainly wouldn’t give that answer for an interview!
Mutt.
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BFL again a very hot topic. I´m for CAP 56 point of view, but I disagree about that the stopway is always a clearway. The clearway must be at least 500 feet wide while stopway must be at least runway widht (tipically 120-150 feet).
Clearway covers airbone path with engine-out directional problems, while stopway just cover RTO .
Clearway covers airbone path with engine-out directional problems, while stopway just cover RTO .